Heretofore numerous types of anti-skid devices have been known in the aviation and transportion industries. Particularly, such devices are most desirable for use in aircraft when high speeds, short braking distances, large inertia and human lives are involved. Consequently, most commercial and military aircraft are presently provided with anit-skid systems for guaranteeing that braking effort is, for any given situation, optimized. Such systems operate on the premise that the most effective braking effort is achieved by allowing the brake application to "hunt" about incipient skid conditions. When major skids occur, the brake pressure in most systems is completely dumped to allow the wheels to spin back up to runway speeds before reapplication of brake pressure under control of the anti-skid system.
Presently known systems generally provide so-called fail-safe means whereby control of braking is completely returned to the aircraft pilot in the event that the antiskid system causes brake pressure to be fully dumped for a period of time exceeding a preset limit (for example, two seconds) since such a condition is associated with system failure. In known systems, the reverting of the braking back to the pilot totally disarms the anti-skid system, and brake pressure from then on is totally under control of the pilot. Unfortunately, when the control of the braking effort is returned to the pilot, the degree of brake pedal depression by the pilot (which until then has been overridden by the antiskid system) represents nearly total brake force capacity for the vehicle. Skidding, blowouts, damaged tires and danger to human life is generally the result. Further, aquaplaning of the vehicle's wheels or other extremely adverse runway conditions may also result in the full-dump output of the anti-skid system being interpreted as a system failure. However, with present fail-safe devices the operation of the anti-skid systems, once removed, is not restored to the braking system even after the aquaplaning or adverse runway conditions are over.
Consequently, it is an object of the instant invention to present a failure warning and shut-off for anti-skid systems wherein there is not an instantaneous return of total braking to the pilot following either the adverse conditions mentioned above or anti-skid circuit failure.
Yet another object of the invention is to present a failure warning and shut-off for anti-skid systems wherein the anti-skid system, though released of operation during specific periods of adverse operation, may resume operation after satisfying certain conditions.
Still another object of the invention is to present a failure warning and shut-off for anti-skid systems wherein the overriding of the anti-skid system is, in such situations, carefully monitored and supplemented by a rudimentary anti-skid system.
Another object of the invention is to present a failure warning and shut-off for anti-skid systems wherein certain kinds of adverse operation of the anti-skid system may be rapidly negated without the subsequent inherent dangers of locked brakes, blown or damaged tires, or danger to human lives.
Yet another object of the invention is to present a failure warning and shut-off for anti-skid systems wherein the pilot is immediately informed of the shut-off of operation of the normal anti-skid system.
Still another object of the invention is to present a failure warning and shut-off for anti-skid systems which is reliable and accurate in operation, inexpensive to construct, easily adaptable for implementation with state of the art anti-skid systems, and readily constructed from available components.
These objects and other objects which will become apparent as the detailed description proceeds are achieved by: an improvement in a wheeled vehicle having anti-skid circuitry associated with the wheels thereof for producing anti-skid signals indicative of conditions of non-rotation of the wheels and for applying the anti-skid signals to anti-skid valves for the wheels, said improvement comprising: a comparator connected to the anti-skid circuitry and producing an output signal when the anti-skid signals exceed a particular level for a particular time duration; a pulse generator; and a switching circuit interconnected between said pulse generator and the anit-skid circuitry and controlled by said comparator to interconnect the anti-skid valves with the pulse generator upon receipt of said output signals and simultaneously disconnect the anti-skid circuitry from the anti-skid valves.